Recent requirements have led to detecting a load of an occupant seated on a seat cushion by means of a plurality of load sensors and controlling of operations of an air bag in accordance with a weight of an occupant, which is disclosed in WO2006/011597 (hereinafter, referred to as reference 1), for example. As one of the examples, with reference to FIG. 12, each load sensor disclosed in reference 1 includes a sensor portion 100, an amplifying circuit 101, a digital circuit 102, and a memory 103. The sensor portion 100 is formed by a Wheatstone bridge structured by four strain gauges. A strain generated by the occupant seated on the seat cushion is converted to an electric resistance by strain gauges. The electric resistance is converted to an electric voltage by the Wheatstone bridge. The amplifying circuit 101 amplifies the electric voltage outputted from the sensor portion 100. The digital circuit 102 converts the electric voltage outputted from the amplifying circuit 101 to a digital value and sends the digital value to a processing device. The memory 103 is employed for memorizing a sensitivity AS, which will be described later.
An adjustment of the load detecting sensitivity of the seat for the vehicle is implemented to each load sensor. In the beginning, zero point adjustment is performed when no load is applied to each load sensor. Then, as illustrated in FIG. 12, two sensitivities A1 and A2 are provisionally set, and points P1, P2, P3 and P4 respectively representing sensor output of the load sensor are obtained. Here, each of the points P1 and P3 represents the sensor output when no load is applied to the load sensor, while each of the points P2 and P4 represents the sensor output when a rated load is applied to the load sensor. Afterward, the optimal sensitivity AS is obtained on the basis of a designed value LO under no load being applied to the load sensor and a designed value UP under the rated load being applied to the load sensor. Then, the optimal sensitivity AS is memorized in the memory 103.
According to the seat for the vehicle with the load sensors respectively adjusted as described above, when the occupant is practically seated on the seat for the vehicle, the load of the occupant is precisely detected by correcting and totaling each output of each load sensor by the optimal load sensitivity AS.
However, according to the adjusting method of the load detecting sensitivity of the seat for the vehicle described above, the optimal sensitivity AS is required to be obtained from every load sensor. Further, in order to obtain the optimal sensitivity AS, the sensor output is required to be obtained at both of the provisionally set sensitivities A1 and A2 in accordance with a case where no load is applied to each load sensors and a case where the rated load is applied to each load sensors. Therefore, equipment cost and adjusting cost may be increased. In addition, an examining process is provided as a posterior process of an adjusting process described above. However, the tact time of the adjusting process is longer than that of the examining process. Accordingly, in order to adjust both tact times of the examination process and of the adjusting process, a plurality of adjustment equipments is required relative to one examination equipment, thus leading to an increase of the equipment cost and adjustment cost.
A need thus exists for a method for adjusting the load detecting sensitivity of a seat for a vehicle which is not susceptible to the drawback mentioned above.